ABSTRACT The Planning for the HEALthy Early Development Study will contribute to the design and recommended protocol for a future large-scale, multi-site research study to prospectively examine human brain, cognitive, behavioral, social and emotional development of children beginning prenatally through ages 9-10, and to determine the impact of maternal pre- and postnatal substance use on short- and long-term development of children. The Planning Study will link investigators across 6 research sites who have complementary experience and expertise in the areas that are essential to designing the study. Planning activities will be accomplished using a coordinated set of 10 Working Groups who will work collaboratively to design a sampling and recruitment strategy for a future large-scale study, to identify and recommend strategies for addressing the challenges to ethical recruitment and retention of vulnerable populations, and to develop and test a common protocol for neuroimaging, infant and child assessments, exposure assessment, biospecimen collection, and integration of novel technologies. By the end of the Planning Phase, the 6 Consortium sites will have produced and tested a recommended protocol for the future multi-site study, and will have established feasibility of carrying out the study protocol at each of the 6 linked sites.